Android Code Security — Part I
To begin with, we are going to enumerate the different parts of the architecture in Android.
- Linux Kernel, which is an interface that provides a way to interact between the OS and the hardware of the device.
- Libraries, (C/C++ Native) for the following capabilities: 3D/2D, media (mp3, photos), SSL, sqlite…
- Runtime, core runtime libraries that provide most of the functionality of the Java programming language,and Dalvik VM/ART, to execute the applications.
- Java Framework, all the Android OS functions are available using APIs in Java. These contains the different components thatare used to develop Android Applications: Content Providers, Activities…
- System Apps, are included by default in the devices, they provide esential capabilities that can be accessed by the applications developed, like SMS, Camera, Browser…
Types of Android Applications
- Native apps: written for the specific platform. In Android is in Java or Kotlin.
Some of the advantages of native apps are:
- Hybrid apps: written in multiple platforms.
Some of the advantages of hybrid apps are:
How are Android Apps
Android apps are developed in Java and bytecode-compiled into a DEX format.
This bytecode is interpreted by Android Virtual Machine to be rendered in the device.
- Android <= 4.4 (Kitkat) : Dalvik Virtual Machine (DVM)
- Android 5 (Lollipop): Android Runtime (ART)
Components of an Android App
An Android App is a file with .APK extension. This is essentially a compressed file with a determined structure.
- Manifest
- Signatures
- Assets
- Resources
- Compiled resources
- Native libraries
- Dalvik Bytecode
Security Assessment for Android Apps
To end this post, there are two types of security assesments to have full knowledge of the security of an application:
- Static analysis: source code analysis.
- Dinamic analysis: requires execution of the application.
In an Android security assesment, there are the following steps:
- Obtain the application to analyze (apk).
- Reversing (decompilation of the code).
- Code analysis.
- Dinamic analysis.
- Results and triage: obtain the different vulnerabilities and remove the false positives (not an issue).
- Results elaboration and report.
In the next post, there will be an explanation of each of the steps.
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Also, I will give you a link of an application that performs all the security assesment and malware analysis of an Android Application automatically.
